1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to drive arrangements for elevator systems having an AC drive motor.
2. Description of the Prior Art
Traction elevator systems which operate at speeds above about 500 feet per minute are directly driven by a DC motor. Systems which operate below 500 feet per minute utilize a reduction gear and either an AC or a DC drive motor. DC drive motors provide good control and thus a smooth ride and are usually used in geared applications when ride quality is important. DC drives for elevators are more costly than AC drives, however, and considerable effort has been directed to improving the performance of AC drives for elevators using thyristor control. However, the more sophisticated the AC control, the less its cost advantage over the DC drive. Thus, it would be desirable to provide a new and improved elevator system having an AC drive arrangement which provides a smooth ride while utilizing a minimum of feedback and AC control.